Antennas have been devised for use with mobile or portable communications devices, including cellular telephones. Various antenna types are used, including monopole, dipole, loop and patch antennas. Each antenna has particular advantages and drawbacks which are considered by designers when choosing an antenna for a specific application.
When used for receiving purposes, antennas may operate in the presence of multi-path signals, and with signal wave-fronts of arbitrary polarization with respect to a characteristic polarization of an antenna element. The received signal amplitude for each antenna element is thus often characterized by a time-dependent property associated with a changing multi-path environment or with the motion of the receiver, which may lead to reception difficulties if the received signal becomes too weak.
Generally, the received signals may be characterized as having a spatially and temporally varying field strength comprised of an E-field (electrical field) and an H-field (magnetic field). Various antenna configurations may be considered to optimize the received signal strength, including diversity configurations, such as space diversity, polarization diversity and pattern diversity.
In many applications, the size of the antennas is small and each of the antennas may not be optimized for the frequency being used, leading to further losses in received signal strength. This may also reduce the power which may be effectively transmitted.